In a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE)/LTE-Advanced (LTE-A) system, an orthogonal frequency division multiple access (OFDMA) manner is generally used as a downlink multiple access manner. A downlink resource of the system is divided into subframes in a time domain, and is divided into subcarriers in a frequency domain. In a current LTE system, duration of one subframe is 1 millisecond (ms), and each subframe is further divided into two slots (slot) of 0.5 ms. For a normal cyclic prefix (normal CP), each slot consists of seven orthogonal frequency division multiplexing (OFDM) symbols. For an extended cyclic prefix (extended CP), each slot consists of six OFDM symbols. The OFDM symbol is hereinafter referred to as a symbol.
Generally, a base station may perform uplink channel estimation by using a reference signal such as a demodulation reference signal (DMRS). The DMRS exists on a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH). A time domain location of the DMRS on the PUSCH is the fourth symbol, from the bottom, of each slot, and a frequency domain location is consistent with bandwidth allocated to a user. A location on the PUCCH varies with a PUCCH transmission format.
In future communication, there is a quite high requirement for a quantity of user connections, and frequently sending a small data packet poses a challenge to a control channel capacity. As shown in FIG. 1, in order to reduce resources occupied by control signaling, system bandwidth/frequency domain resources are divided into two parts. One part is a scheduling area, and the other part is a competitive data transmission area without control channel scheduling. Using an uplink PUSCH as an example, a base station designates some terminal devices to send control signaling in the competitive transmission area, and the base station receives data by means of blind detection.
Because there is no indication of the control signaling in the competitive data transmission area, the terminal device can be associated only with a DMRS. If DMRSs associated with two terminal devices are the same and sent at the same time, the base station cannot correctly obtain channels of the two terminal devices by using the DMRSs. This causes a severe decrease in detection performance.
An uplink DMRS pilot sequence in an existing LTE system is a Zadoff-Chu sequence. A plurality of DMRS sequences are generated by using different shifts of one root sequence, and each DMRS sequence corresponds to one terminal device in one time interval. In the existing system, to ensure orthogonality between different uplink DMRS sequences, a maximum of eight shifts are used in the Zadoff-Chu sequence. That is, in an existing communication mechanism, a maximum of eight users can be allowed to send uplink data in the competitive data transmission area in a same time interval. This is far from meeting a requirement for the connections of a plurality of users.